What do you guys recommend or do to make sure carbon does not delaminate from plastic ie bumpers?

It really depends on the type of plastic you're bonding to. The bond of epoxy to ABS can be improved by flame-treating the ABS. I'd recommend running some trials through because often no much prep is necessary to result in a good bond. However, there are some *really* difficult to bond to plastics which epoxy simply won't touch (think polypropylene, polyethylene) which would either need some very specialist priming or to be avoided altogether.